Original Article The Role of Morningness and Endurance in Mood and Attention During Morning and Evening Hours Konrad S. Jankowski and Marcin Zajenkowski Faculty of Psychology, University of Warsaw, Poland Abstract. This study aimed at testing the effects of morningness-eveningness and endurance on mood and selective attention during morning and evening hours. University students (N = 80) completed the Polish version of the Morningness-Eveningness Questionnaire, the Formal Characteristics of Behaviour-Temperament Inventory, and two testing sessions scheduled during the morning and evening hours. Each testing session consisted of completing the UWIST Mood Adjective Checklist composed of three scales: energetic arousal (EA), tense arousal (TA), and hedonic tone (HT), and a computerized visual search task. Without consideration of morningness and endurance, a time-of-day effect appeared in the visual attention but not in affect: participants were more accurate and faster in the evening than in the morning. Considering morningness and endurance, neither of them influenced the selective attention but they did influence mood. Morningness influenced diurnal variations in EA and HT in such a way that from morning to evening hours, morning chronotypes showed a decrease and evening types an increase in EA and HT. During morning hours, morningness was related to higher EA and HTand lower TA, but endurance was not. During evening hours, morningness was unrelated to mood, but endurance was linked to higher EA. It is concluded that morningness and endurance impact mood differently throughout the day, with the role of morningness decreasing and the role of endurance increasing as the day progresses. Keywords: chronotype, owls and larks, Regulative Theory of Temperament, time of day, affect Morningness-eveningness, also termed chronotype, describes individual differences in functioning at different times of day. In more morning oriented people, as com- pared to evening ones, phases of circadian rhythms are shifted toward earlier hours and this shift is considered a temperamental trait with probably the best evidenced bio- logical basis among various traits studied in the field of dif- ferential psychology. Individual differences in chronotype can be observed not only in human beings, but also in ani- mal world, for instance, in other mammals (e.g., rodents; Vivanco, Rol, & Madrid, 2010), birds (Lehmann, Spoelstra, Visser, & Helm, 2012), or insects (Vaze, Kannan, Abhilash, & Sharma, 2012). Genetic factors explain around 50% of the variance in human morningness-eveningness (Koskenvuo, Hublin, Partinen, Heikkilä, & Kaprio, 2007), and they are related to polymorphisms in clock genes (Pedrazzoli et al., 2010). On the physiological level, even- ing oriented individuals, as compared to morning ones, have longer period of the free running intrinsic circadian rhythm (tau) (Emens et al., 2009) generated by the biolog- ical clock – anatomical structure located in the suprachias- matic nuclei (Dijk & Lockley, 2002); the same location of biological clock and relationships between tau and chrono- type are also observed in animals (Sládek, Polidarová, Nováková, Parkanová, & Sumová, 2012). In people with longer free running tau (exceeding typical value of 24.2 hr) activity and sleep tend to drift toward later hours, particularly when they are released from social obligations (e.g., on free days). Among other biological determinants of morningness-eveningness, the role of age is well proven; during adolescence a shift toward eveningness is observed, and then a shift back to morningness from early adulthood to old age appears (Jankowski, 2015). Chronotype is also influenced by environmental factors, with light being the best documented agent both in human beings (Jankowski, Vollmer, Linke, & Randler, 2014; Roenneberg, Kantermann, Juda, Vetter, & Allebrandt, 2013) and animals (Vivanco et al., 2010). Apart from ongoing influences of light on circadian functioning, some effects of postnatal light exposure have been reported (Tonetti, Fabbri, Martoni, & Natale, 2011). Also, social activity has been recognized as an important synchronizer, even in animals (Favreau, Richard-Yris, Bertin, Houdelier, & Lumineau, 2009), but recently it was argued that the action of social Zeitgeber is actually mediated by light exposure (Roenneberg et al., 2013), for example, people forced to go to work early in the morning are exposed to early sunlight, what shortens their tau to 24 hr. Overall, morningness-eveningness meets requirements to be consid- ered a temperamental trait (Strelau, 2008), that is, has well- established biological background, exists in animal world, though it can be partly influenced by environmental factors. Morningness has been related to a number of individual characteristics, such as a better school performance Ó 2016 Hogrefe Publishing Journal of Individual Differences 2016; Vol. 37(2):73–80 DOI: 10.1027/1614-0001/a000189 http://econtent.hogrefe.com/doi/pdf/10.1027/1614-0001/a000189 - Konrad Jankowski <konrad.jankowski@psych.uw.edu.pl> - Tuesday, June 14, 2016 1:59:12 AM - IP Address:89.77.199.122